Tk_GetUserInactiveTime returns the number of milliseconds that
have passed since the last user interaction (usually via keyboard or
mouse) with the respective display. On systems and displays that do not
support querying the user inactiviy time, -1 is returned.
Tk_GetUserInactiveTime resets the user inactivity timer of the
given display to zero. On windowing systems that do not support
multiple displays display can be passed as NULL.